Polishing end point detection method and polishing end point detection apparatus

ABSTRACT

There is provided a polishing end point detection method of improving the accuracy of detecting a polishing end point. The polishing end point detection method emits light toward a polishing object including a hybrid film made of a nanocarbon material and a light-transmissive material while polishing the polishing object (Step S 102 ). Then, the polishing end point detection method receives light reflected from the polishing object (Step S 103 ). Then, the polishing end point detection method subjects the received reflected light to signal processing (Step S 104 ). Then, the polishing end point detection method determines the polishing end point of the polishing object based on the result of the signal processing (Step S 105 ), and detects the polishing end point (Step S 106 ).

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of theprior Japanese Patent Application No. 2013-271413, filed on Dec. 27,2013, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a polishing end point detection methodand a polishing end point detection apparatus.

2. Description of the Related Art

Examples of conventional wiring materials for semiconductor circuits andthe like include copper, tungsten, and the like. A reduction in size ofsuch a semiconductor circuit involves an increase in electricalresistance of such a wiring material. As a result, a reduction incurrent capacity may cause a problem of reduction in reliability. Inlight of this, as a next generation wiring material, attention has beenpaid to a nanocarbon material expected to have low resistance and highreliability even for thin line widths.

Examples of the nanocarbon material include a multilayer graphene (MLG)made of graphene sheets stacked thereon and a carbon nanotube (CNT). TheMLG is used, for example, as a horizontal wiring of the semiconductorcircuit. The carbon nanotube is used, for example, as a vertical wiring(via) of the semiconductor circuit.

The surface of a substrate such as a semiconductor wafer containing awiring of the nanocarbon material is polished by a polishing apparatussuch as a chemical mechanical polishing (CMP) apparatus. When thesubstrate is polished by the polishing apparatus, the polishing endpoint is determined.

To this end, according to a conventional technique disclosed in JapanesePatent Laid-Open No. 10-202523, the polishing end point is visuallyinspected by a human operator. More specifically, when a predeterminedtime has elapsed since polishing started, the operator stops polishingand visually inspects the surface of the substrate (e.g., for the colorand the like of the substrate surface). If the operator determines thatpolishing is insufficient as a result of visual inspection, the operatorstarts polishing again. Then, when a predetermined time has elapsedsince polishing started, the operator stops polishing and visuallyinspects the surface of the substrate. According to such a conventionaltechnique, an optimal polishing end point is determined by repeating thepolishing and the visual inspection.

SUMMARY OF THE INVENTION

The conventional technique does not consider improving the accuracy ofdetecting the polishing end point.

Specifically, in the conventional technique, polishing end points varybecause the operator visually inspects the polishing end point. Inaddition, the visual inspection by the operator may increase man-hoursbecause the operator needs to repeat polishing and visual inspection.Alternatively, in order to check the polished state, destructionobservation using cross-sectional SEM may conventionally be used toinspect the film thickness of the substrate. However, this methodinvolves destruction of the substrate and hence cannot be used in a stepof producing actual products.

It is therefore an object of an aspect of the present invention toimprove the accuracy of detecting the polishing end point.

An aspect of a polishing end point detection method of the presentinvention has been made in view of the above problem and comprises thesteps of: emitting light to a polishing object including a hybrid filmmade of a nanocarbon material and a light-transmissive material whilepolishing the polishing object; and detecting a polishing end point ofthe polishing object based on light reflected from the polishing object.

In an aspect of the polishing end point detection method of the presentinvention, the step of detecting the polishing end point of thepolishing object may detect the polishing end point of the polishingobject using optical interferometry for measuring a film thickness ofthe polishing object based on a phase difference in light reflected fromthe polishing object.

In an aspect of the polishing end point detection method of the presentinvention, the step of detecting the polishing end point of thepolishing object may detect the polishing end point of the polishingobject based on a change in intensity of a composite wave obtained bycombining the light reflected from a plurality of reflecting surfaces ofthe polishing object and a polishing rate of the polishing object.

In an aspect of the polishing end point detection method of the presentinvention, the step of detecting the polishing end point may detect thepolishing end point of the polishing object based on a change in opticalspectrum of the light reflected from the polishing object.

In an aspect of the polishing end point detection method of the presentinvention, the step of detecting the polishing end point may detect thepolishing end point of the polishing object based on a result ofcomparison between a preset optical spectrum waveform and an opticalspectrum waveform of the light reflected from the polishing object.

In an aspect of the polishing end point detection method of the presentinvention, the nanocarbon material may include a graphene sheet or acarbon nanotube.

An aspect of a polishing end point detection apparatus of the presentinvention comprises: a light emitting unit configured to emit lighttoward a polishing object including a hybrid film made of a nanocarbonmaterial and a light-transmissive material; a light receiving unitconfigured to receive light reflected from the polishing object; and adetection unit configured to detect the polishing end point of thepolishing object based on the light received by the light receivingunit.

In an aspect of the polishing end point detection apparatus of thepresent invention, the detection unit may detect the polishing end pointof the polishing object using optical interferometry for measuring afilm thickness of the polishing object based on a phase difference inlight reflected from the polishing object.

In an aspect of the polishing end point detection apparatus of thepresent invention, the detection unit may detect the polishing end pointof the polishing object based on a change in intensity of a compositewave obtained by combining the light reflected from a plurality ofreflecting surfaces of the polishing object and a polishing rate of thepolishing object.

In an aspect of the polishing end point detection apparatus of thepresent invention, the detection unit may detect the polishing end pointof the polishing object based on a change in optical spectrum of thelight reflected from the polishing object.

In an aspect of the polishing end point detection apparatus of thepresent invention, the detection unit may detect the polishing end pointof the polishing object based on a result of comparison between a presetoptical spectrum waveform and an optical spectrum waveform of the lightreflected from the polishing object.

In an aspect of the polishing end point detection apparatus of thepresent invention, the nanocarbon material may include a graphene sheetor a carbon nanotube.

Such an aspect of the present invention can improve the accuracy ofdetecting the polishing end point.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view schematically illustrating an entire structure of thepolishing apparatus and the polishing end point detection apparatus;

FIG. 2A is a view for describing a measurement principle of opticalinterferometry;

FIG. 2B is a view for describing the measurement principle of opticalinterferometry;

FIG. 3 is a view for describing the measurement principle of opticalinterferometry;

FIG. 4A is a view illustrating an outline of processing of a signalprocessing unit;

FIG. 4B is a view illustrating an outline of processing of the signalprocessing unit;

FIG. 4C is a view illustrating an outline of processing of the signalprocessing unit;

FIG. 5 is a view illustrating an outline of wiring using an MLG and acarbon nanotube;

FIG. 6A is a view schematically illustrating an example of a circuitusing the carbon nanotubes;

FIG. 6B is a view schematically illustrating an example of the circuitusing the carbon nanotubes;

FIG. 6C is a view schematically illustrating an example of the circuitusing the carbon nanotubes;

FIG. 7 is a view simply modeling the example of the circuit using thecarbon nanotubes;

FIG. 8 is a flowchart illustrating a flow of a process of detecting apolishing end point;

FIG. 9A is a graph illustrating a change in optical spectrum ofreflected light from a substrate modeled in FIG. 7, which has beenpolished seven times while polished repeatedly, each process ofpolishing the substrate continuing for 240 seconds;

FIG. 9B is a graph illustrating a change in optical spectrum ofreflected light from a substrate modeled in FIG. 7, which has beenpolished seven times while polished repeatedly, each process ofpolishing the substrate continuing for 240 seconds;

FIG. 9C is a graph illustrating a change in optical spectrum ofreflected light from a substrate modeled in FIG. 7, which has beenpolished seven times while polished repeatedly, each process ofpolishing the substrate continuing for 240 seconds; and

FIG. 10 is a graph illustrating an example of detecting the polishingend point using a spectral index waveform.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a polishing end point detection method and a polishing endpoint detection apparatus according to an embodiment of the presentinvention will be described with reference to the accompanying drawings.

FIG. 1 is a view schematically illustrating an entire structure of thepolishing apparatus and the polishing end point detection apparatus. Thedescription starts with the polishing apparatus.

As illustrated in FIG. 1, a polishing apparatus 100 includes a polishingtable 110, on an upper surface of which a polishing pad 108 can bemounted so as to polish a substrate 102 such as a semiconductor wafer.The polishing apparatus 100 further includes a first electric motor 112rotationally driving the polishing table 110. The polishing apparatus100 furthermore includes a top ring 116 capable of holding the substrate102. The polishing apparatus 100 still further includes a secondelectric motor 118 rotationally driving the top ring 116.

The polishing apparatus 100 further includes a slurry line 120 on anupper surface of the polishing pad 108. The slurry line 120 supplies apolishing liquid containing a polishing agent. The polishing apparatus100 furthermore includes a polishing apparatus control unit 140outputting various control signals about the polishing apparatus 100.

When the substrate 102 is polished, the polishing apparatus 100 suppliespolishing slurry containing abrasive grains onto the upper surface ofthe polishing pad 108 through the slurry line 120 and the first electricmotor 112 rotationally drives the polishing table 110. Then, thepolishing apparatus 100 presses the substrate 102 held by the top ring116 against the polishing pad 108 in a state in which the top ring 116is rotated about a rotation axis eccentric to a rotation axis of thepolishing table 110. This allows the substrate 102 to be polished andplanarized by the polishing pad 108 holding the polishing slurry.

The description now focuses on the polishing end point detectionapparatus. As illustrated in FIG. 1, a polishing end point detectionapparatus 200 includes an optical sensor 210. The polishing end pointdetection apparatus 200 further includes an end point detectionapparatus body 220 connected to the optical sensor 210 through rotaryjoint connectors 160 and 170.

The present embodiment uses optical interferometry to measure the filmthickness of the substrate 102 and to detect the polishing end point ofthe substrate 102. Here, the measurement principle of the opticalinterferometry will be briefly described.

FIGS. 2A, 2B, and 3 each are a view for describing the measurementprinciple of the optical interferometry. An example used herein assumesthat a polishing film 320 to be polished is stacked on a siliconsubstrate 310. First, as illustrated in FIG. 2A, after incident light(n0) is emitted from the optical sensor 210, reflected light R1 isreflected on a surface of the polishing film 320 and reflected light R2is transmitted through the polishing film 320 and reflected on aninterface between the polishing film 320 and the silicon substrate 310.Then, the reflected light R1 is combined with the reflected light R2.Note that the reflected light R1 and the reflected light R2 have thesame phase.

Next, as illustrated in FIG. 2B, even after the film thickness of thepolishing film 320 is changed, the reflected light R1 is reflected on asurface of the polishing film 320 and the reflected light R2 istransmitted through the polishing film 320 and reflected on an interfacebetween the polishing film 320 and the silicon substrate 310. Then, thereflected light R1 is combined with the reflected light R2. Note thatthe reflected light R1 and the reflected light R2 have reverse phases toeach other. Thus, it is understood from FIGS. 2A and 2B that a change inthe film thickness of the polishing film 320 due to polishing generatesa phase shift between the reflected light R1 and the reflected light R2.

FIG. 3 is a graph illustrating a transition in the signal intensity of acomposite wave obtained by combining the reflected light R1 and thereflected light R2. In FIG. 3, the abscissa axis represents the filmthickness of the polishing film 320, and the ordinate axis representsthe signal intensity of the composite wave obtained by combining thereflected light R1 and the reflected light R2. A change in the filmthickness of the polishing film 320 due to polishing generates a phaseshift between the reflected light R1 and the reflected light R2according to a change in the film thickness. This, in turn, leads to aperiodic change in the reflection intensity of the composite wave asillustrated in FIG. 3. Note that in FIG. 3, (1) represents a portionwhere the reflected light R1 and the reflected light R2 have the samephase as illustrated in FIG. 2A, and (2) represents a portion where thereflected light R1 and the reflected light R2 have reverse phases toeach other as illustrated in FIG. 2B.

The polishing end point detection apparatus 200 measures the filmthickness of the polishing film 320 and detects the polishing end pointof the polishing film 320 based on the transition in the signalintensity of the composite wave. For example, if the relationshipbetween the polishing rate of the polishing film 320 and the period ofthe transition in the signal intensity of the composite wave is known,the polishing end point detection apparatus 200 can measure thepolishing amount of the polishing film 320 and detect the polishing endpoint of the polishing film 320.

Referring now back to FIG. 1, the polishing end point detectionapparatus 200 will be specifically described. The optical sensor 210includes a light emitting unit emitting light toward the substrate 102;and a light receiving unit receiving light reflected from the substrate102. Here, a hole is formed in the polishing table 110 and the polishingpad 108 so as to insert the optical sensor 210 thereinto from a rearsurface side of the polishing table 110. The optical sensor 210 isinserted into the hole formed in the polishing table 110 and thepolishing pad 108. The optical sensor 210 emits light toward thesubstrate 102 and receives light reflected from the substrate 102.

The end point detection apparatus body 220 includes a spectroscope 230,a signal processing unit 240, and a polishing end point detection unit250. The spectroscope 230 receives the reflected light from the opticalsensor 210. The spectroscope 230 splits the reflected light for eachwavelength (e.g., 400 nm to 800 nm).

The signal processing unit 240 calculates the spectral indexrepresenting the intensity of the reflected light for each predeterminedinterval (e.g., one rotation of the polishing table 110) along thepolishing time. The signal processing unit 240 calculates the spectralindex waveform obtained by plotting the calculated spectral index intime sequence.

The description will now focus on the processing of the signalprocessing unit 240. FIGS. 4A, 4B, and 4C each are a view illustratingan outline of processing of the signal processing unit 240. First, asillustrated in FIG. 4A, the signal processing unit 240 calculates thesignal intensity of the reflected light of each wavelength for eachpredetermined interval (e.g., one rotation of the polishing table 110)along the polishing time. Then, as illustrated in FIG. 4B, the signalprocessing unit 240 calculates the spectral index for each predeterminedinterval based on the signal intensity of the reflected light of eachwavelength for each predetermined interval. Then, as illustrated in FIG.4C, the signal processing unit 240 calculates the spectral indexwaveform by plotting the spectral index of each predetermined intervalin time sequence.

Referring back to FIG. 1 again, the polishing end point detection unit250 detects the polishing end point of the substrate 102 based on thelight received by the optical sensor 210 (light receiving unit).Specifically, the polishing end point detection unit 250 detects thepolishing end point of the substrate 102 using optical interferometryfor measuring the film thickness of the substrate 102 based on the phasedifference in light reflected from the substrate 102. For example, asdescribed above in FIG. 3, the polishing end point detection unit 250may detect the polishing end point of the polishing object based on thechange in intensity of the composite wave obtained by combining thelight reflected from a plurality of reflecting surfaces of the polishingobject and the polishing rate of the polishing object.

Alternatively, the polishing end point detection unit 250 may detect thepolishing end point of the substrate 102 based on the change in theoptical spectrum of the light reflected from the substrate 102. Forexample, the polishing end point detection unit 250 compares a presetoptical spectrum waveform with the optical spectrum waveform of thelight reflected from the polishing object. Then, the polishing end pointdetection unit 250 may detect the polishing end point of the polishingobject based on the result of comparison. This method will be describedlater.

The polishing end point detection unit 250 is connected to a polishingapparatus control unit 140 performing various controls about thepolishing apparatus 100. When the polishing end point of the substrate102 is detected, the polishing end point detection unit 250 outputs asignal to that effect to the polishing apparatus control unit 140. Whenthe signal indicating the polishing end point is received from thepolishing end point detection unit 250, the polishing apparatus controlunit 140 stops polishing by the polishing apparatus 100.

The description will now focus on the substrate 102 to be polished inthe present embodiment. According to the present embodiment, thesubstrate 102 includes a hybrid film made of a nanocarbon material and alight-transmissive material.

The nanocarbon material used herein includes a graphene sheet or acarbon nanotube. The graphene sheet is a sheet-like substance having ahexagonal lattice structure like honeycomb made of carbon atoms andtheir bonds. For example, a multilayer graphene (MLG) made of graphenesheets stacked thereon is used for horizontal wiring of a semiconductorcircuit.

In addition, the carbon nanotube is a substance of the graphene sheetwith a single-layered or multilayered coaxial tubular shape. The carbonnanotubes are used, for example, as a vertical wiring (via) of thesemiconductor circuit.

FIG. 5 is a view illustrating an outline of wiring using an MLG and acarbon nanotube. As illustrated in FIG. 5, the wiring of thesemiconductor circuit includes horizontal wirings 410 containing MLG andvertical wirings (vias) 420 containing carbon nanotubes.

The description will now focus on a specific circuit structure. FIGS.6A, 6B, and 6C each are a view schematically illustrating an example ofthe circuit using the carbon nanotubes.

As illustrated in FIG. 6A, the circuit includes a metal film 510 made ofcopper (Cu), tungsten (W), or the like; a nitride film 520 stacked onthe metal film 510; and an oxide film 530 stacked on the nitride film520. A hole (via) for vertical wiring is formed in part of the oxidefilm 530. An underlying film 540 (e.g., Ti or TiN) is formed on theoxide film 530 and in a portion of the oxide film 530 where the hole isformed. A catalyst layer 550 (e.g., Ni or Co) for growing carbonnanotubes is formed on the underlying film 540. Carbon nanotubes 560 areformed grown in a vertical direction on the catalyst layer 550. Further,a hybrid layer 570, in which the carbon nanotubes 560 have beenimpregnated with a light-transmissive material 590 (e.g., spin on glass(SOG)), is formed on the catalyst layer 550. Furthermore, an SOG layer580, which is a single layer of the light-transmissive material 590, isformed on the hybrid layer 570. The SOG film used in the hybrid layer570 and the SOG layer 580 is an example of the light-transmissivematerial 590. Note that the present embodiment has described an exampleof using an SOG film for the hybrid layer 570 and the SOG layer 580, butnot limited thereto, and any substance can be used as long as thesubstance can transmit light and can impregnate the carbon nanotubes 560therewith. Note also that the following description will focus ondetecting the polishing end point of a substrate including the carbonnanotubes and the light-transmissive material, but not limited thereto,and the present embodiment can be applied to detecting the polishing endpoint of a substrate including other carbon nanotube material (such asMLG) and the light-transmissive material.

Here, assume that the substrate is polished in the order of FIGS. 6A,6B, and 6C, until the polishing end point is reached at the state ofFIG. 6C. FIG. 7 is a view simply modeling the example of the circuitusing the carbon nanotubes.

As illustrated in FIG. 7, the modeled circuit includes a siliconsubstrate 610; a TEOS (insulating film) layer 620 stacked on the siliconsubstrate 610; and an underlying layer 630 made of TiN and Ti stacked onthe TEOS layer 620. The modeled circuit further includes a catalystlayer 660 made of Ni stacked on the underlying layer 630. The modeledcircuit furthermore includes a hybrid layer 640 mixing the carbonnanotubes and SOG and being stacked on the catalyst layer 660. Themodeled circuit still furthermore includes an SOG layer 650 stacked onthe hybrid layer 640. Note that the catalyst layer 660 is a very thinlayer (e.g., 2 to 3 nm) and is turned into fine particles when carbonnanotubes are grown. For this reason, the catalyst layer 660 has littleeffect on detection of the polishing end point according to the presentembodiment.

The description will now focus on the process of detecting the polishingend point in the modeled circuit. FIG. 8 is a flowchart illustrating aflow of the process of detecting the polishing end point. First, thepolishing apparatus control unit 140 starts polishing the substrate 102(Step S101). Then, the optical sensor 210 emits light from the lightemitting unit (Step S102). Then, the light receiving unit of the opticalsensor 210 receives light reflected from the substrate 102 (Step S103).

Then, the signal processing unit 240 subjects the reflected light tosignal processing (Step S104). Specifically, as illustrated in FIG. 4A,the signal processing unit 240 calculates the signal intensity of thereflected light of each wavelength for each predetermined interval(e.g., one rotation of the polishing table 110) along the polishingtime. Then, as illustrated in FIG. 4B, the signal processing unit 240calculates the spectral index for each predetermined interval based onthe signal intensity of the reflected light of each wavelength for eachpredetermined interval. Then, as illustrated in FIG. 4C, the signalprocessing unit 240 calculates the spectral index waveform by plottingthe spectral index of each predetermined interval in time sequence.

Then, based on a result of the signal processing in Step S104, thepolishing end point detection unit 250 determines the polishing endpoint (Step S105). For example, the polishing end point detection unit250 may determine the polishing end point of the substrate 102 based onthe change in the optical spectrum of the reflected light.

The above process will be described as follows. FIGS. 9A, 9B, and 9Ceach are a graph illustrating a change in optical spectrum of reflectedlight from the substrate modeled in FIG. 7, which has been polishedseven times while polished repeatedly, each process of polishing thesubstrate continuing for 240 seconds. In FIGS. 9A, 9B, and 9C, theabscissa axis represents the wavelength of light, and the ordinate axisrepresents the signal intensity of the reflected light. Note thataccording to the present embodiment, the film thickness of the TEOSlayer 620 in the central portion of the substrate was checked by a filmthickness measuring device at the end of each polishing. As a result, itwas found that the TEOS layer 620 in the central portion of thesubstrate was hardly scraped at the end of the sixth polishing, but waslargely scraped at the end of the seventh polishing. This leads toconsidering that the CNT-SOG hybrid layer 640, the catalyst layer 660,the underlying layer 630, and the TEOS layer 620 in the central portionof the substrate were scraped off in the seventh polishing.

FIG. 9A is a graph illustrating the waveform of optical spectrum plottedevery 10 rotations from the 10th rotation to the 190th rotation in the7th polishing. In FIG. 9A, the optical spectrum waveform has an up anddown amplitude at a relatively small period.

Then, FIG. 9B is a graph illustrating the waveform of optical spectrumplotted every 10 rotations from the 200th rotation to the 250th rotationin the 7th polishing. In FIG. 9B, the optical spectrum waveform has aless up and down amplitude at a small period, and has an up and downamplitude at a large period.

Further, FIG. 9C is a graph illustrating the waveform of opticalspectrum plotted every 10 rotations from the 260th rotation to the 710throtation in the 7th polishing. In FIG. 9C, the optical spectrum waveformhas little up and down amplitude at a small period, and has an up anddown amplitude at a large period.

Such a change in the waveform of optical spectrum leads to consideringthat, although roughly, the waveform like FIG. 9A appears when theCNT-SOG hybrid layer 640 is polished; the waveform like FIG. 9B appearswhen the catalyst layer 660 or the underlying layer 630 is polished; andthe waveform like FIG. 9C appears when the TEOS layer 620 is polished.

In light of this, when the optical spectrum waveform like FIG. 9C isdetected, the polishing end point detection unit 250 determines that theTEOS layer 620 has started to be polished. When a preset predeterminedtime has elapsed since it was determined that the TEOS layer 620 startedto be polished, the polishing end point detection unit 250 may determineas the polishing end point being reached (detect the polishing endpoint). For example, the optical spectrum waveform like FIG. 9C ispreset, and then the polishing end point detection unit 250 compares thepreset optical spectrum waveform with the optical spectrum waveformcalculated by the signal processing unit 240. When the degree ofmatching between the preset optical spectrum waveform and the opticalspectrum waveform calculated by the signal processing unit 240 isgreater than or equal to a preset threshold, the polishing end pointdetection unit 250 may determine that the TEOS layer 620 has started tobe polished.

Alternatively, the polishing end point detection unit 250 may detect thepolishing end point based on a spectral index waveform. FIG. 10 is agraph illustrating an example of detecting the polishing end point usingthe spectral index waveform.

In FIG. 10, the abscissa axis represents the polishing time, and theordinate axis represents the reflection intensity. For example, thefrequency of the spectral index waveform obtained when the TEOS layer620 is polished is preset. When the spectral index waveform of thepreset frequency appears and a minimum value 710 of the waveform isdetected, the polishing end point detection unit 250 may determine asthe polishing end point being reached. Alternatively, when a maximumvalue 720, not limited to the minimum value 710, is detected, thepolishing end point detection unit 250 may determine as the polishingend point being reached. Still alternatively, when the minimum value 710or the maximum value 720 is detected a plurality of times, the polishingend point detection unit 250 may determine as the polishing end pointbeing reached. Further, when a predetermined time has elapsed since theminimum value 710 or the maximum value 720 was detected (for example, apredetermined time α has elapsed since the maximum value 720 wasdetected), the polishing end point detection unit 250 may determine asthe polishing end point being reached.

Referring now back to FIG. 8, the polishing end point detection unit 250repeats the process in step S105 until the polishing end point isdetected (Step S106: No). If the polishing end point is detected (StepS106: Yes), the polishing end point detection unit 250 sends a messageindicating that the polishing end point has been detected, to thepolishing apparatus control unit 140 (Step S107).

When the message indicating that the polishing end point has beendetected is received from the polishing end point detection unit 250,the polishing apparatus control unit 140 stops polishing the substrate(Step S108).

As described above, the present embodiment can improve the accuracy ofdetecting the polishing end point. Conventional technique for detectingthe polishing end point of a substrate such as a semiconductor wafercontaining a nanocarbon material wiring has been visually implemented bya human operator, resulting in variations in detection of the polishingend point.

In contrast to the above conventional technique, the present embodimentemits light toward a polishing object including a hybrid film made of ananocarbon material and a light-transmissive material while polishingthe polishing object, and detects the polishing end point of thepolishing object based on the light reflected from the polishing object.Therefore, the present embodiment eliminates the need for an operator toperform visual inspection, and thus can improve the accuracy ofdetecting the polishing end point. In addition, the present embodimenteliminates the need for the operator to repeatedly perform polishing andvisual inspection, and thus can reduce man-hours.

In particular, the nanocarbon material is generally black, and thushardly reflects light but absorbs light. For this reason, the nanocarbonmaterial alone has a problem in that it may be difficult to measure thefilm thickness using optical interferometry. In contrast to this, thepresent embodiment uses optical interferometry to measure the polishingobject including the hybrid film made of a nanocarbon material and alight-transmissive material. Therefore, the present embodiment canreflect part of light on a surface of the light-transmissive material,thus allowing for measurement of the film thickness using opticalinterferometry.

Examples of the method of detecting the polishing end point includeusing rotation torque of the polishing table 110. Specifically, therotation torque of the polishing table 110 correlates with the currentflowing in the first electric motor 112 for rotationally driving thepolishing table 110. For example, assume a case of polishing a polishingobject with a first layer and a second layer stacked thereon, whosepolishing rates differ greatly from each other. In this case, a changein the polishing object from the first layer to the second layer greatlychanges the current flowing in the first electric motor 112. Thus, thedetection of the change in the current may detect the start of polishingof the second layer.

In this regard, the substrate to be polished in the present embodimentwas such that the SOG layer 650 had a polishing rate of 180 to 200nm/min, the CNT-SOG hybrid layer 640 had a polishing rate of 150 to 180nm/min, the underlying layer 630 had a polishing rate of 90 to 110nm/min, and the TEOS layer 620 had a polishing rate of 90 to 110 nm/min.

As described above, according to the substrate to be polished in thepresent embodiment, the polishing rate of each layer did not differ somuch, and thus the current flowing in the first electric motor 112 didnot greatly change. Therefore, according to the substrate to be polishedin the present embodiment, it is difficult to apply the method ofdetecting the polishing end point using the rotation torque of thepolishing table 110.

Note that the polishing rate of the CNT-SOG hybrid layer 640 may changeaccording to the density of carbon nanotubes. An increase in the densityof carbon nanotubes reduces the polishing rate. In this case, this leadsto an increase in difference in the polishing rate between the CNT-SOGhybrid layer 640 and the underlying layer, which may change the electricmotor torque due to polishing of the underlying layer, but it isconsidered that torque change is difficult to occur for the reasondescribed below.

In general, the nanocarbon material has a low friction coefficient, andhence is used as lubricant. When the nanocarbon material is used aslubricant, carbon residues occur during polishing and remain on thepolishing pad surface, leaving the surface in a slippery state. For thisreason, the torque values are small as a whole, leading to a possibilitythat the change is less visible even when the underlying layer isexposed to the polishing surface.

In contrast to this, the present embodiment employs a method ofdetecting the polishing end point using optical interferometry. Thus, asillustrated in FIG. 9, a change in the layer to be polished causes theoptical spectrum waveform to be greatly changed. As a result, thepresent embodiment can accurately detect the polishing end point.

REFERENCE SIGNS LIST

-   100 polishing apparatus-   102 substrate-   140 polishing apparatus control unit-   200 polishing end point detection apparatus-   210 optical sensor-   220 end point detection apparatus body-   230 spectroscope-   240 signal processing unit-   250 polishing end point detection unit-   510 metal film-   520 nitride film-   530 oxide film-   540 underlying film-   550 catalyst layer-   560 carbon nanotube-   570 hybrid layer-   580 SOG layer-   590 light-transmissive material-   610 silicon substrate-   620 TEOS layer-   630 underlying layer-   640 hybrid layer-   650 SOG layer

What is claimed is:
 1. A polishing end point detection method comprisingthe steps of: emitting light to a polishing object including a hybridfilm made of a nanocarbon material and a light-transmissive materialwhile polishing the polishing object; and detecting a polishing endpoint of the polishing object based on light reflected from thepolishing object.
 2. The polishing end point detection method accordingto claim 1, wherein the step of detecting the polishing end point of thepolishing object detects the polishing end point of the polishing objectusing optical interferometry for measuring a film thickness of thepolishing object based on a phase difference in light reflected from thepolishing object.
 3. The polishing end point detection method accordingto claim 1, wherein the step of detecting the polishing end point of thepolishing object detects the polishing end point of the polishing objectbased on a change in intensity of a composite wave obtained by combiningthe light reflected from a plurality of reflecting surfaces of thepolishing object and a polishing rate of the polishing object.
 4. Thepolishing end point detection method according to claim 1, wherein thestep of detecting the polishing end point detects the polishing endpoint of the polishing object based on a change in optical spectrum ofthe light reflected from the polishing object.
 5. The polishing endpoint detection method according to claim 4, wherein the step ofdetecting the polishing end point detects the polishing end point of thepolishing object based on a result of comparison between a presetoptical spectrum waveform and an optical spectrum waveform of the lightreflected from the polishing object.
 6. The polishing end pointdetection method according to claim 1, wherein the nanocarbon materialincludes a graphene sheet or a carbon nanotube.
 7. A polishing end pointdetection apparatus comprising: a light emitting unit configured to emitlight toward a polishing object including a hybrid film made of ananocarbon material and a light-transmissive material; a light receivingunit configured to receive light reflected from the polishing object;and a detection unit configured to detect the polishing end point of thepolishing object based on the light received by the light receivingunit.
 8. The polishing end point detection apparatus according to claim7, wherein the detection unit detects the polishing end point of thepolishing object using optical interferometry for measuring a filmthickness of the polishing object based on a phase difference in lightreflected from the polishing object.
 9. The polishing end pointdetection apparatus according to claim 7, wherein the detection unitdetects the polishing end point of the polishing object based on achange in intensity of a composite wave obtained by combining the lightreflected from a plurality of reflecting surfaces of the polishingobject and a polishing rate of the polishing object.
 10. The polishingend point detection apparatus according to claim 7, wherein thedetection unit detects the polishing end point of the polishing objectbased on a change in optical spectrum of the light reflected from thepolishing object.
 11. The polishing end point detection apparatusaccording to claim 10, wherein the detection unit detects the polishingend point of the polishing object based on a result of comparisonbetween a preset optical spectrum waveform and an optical spectrumwaveform of the light reflected from the polishing object.
 12. Thepolishing end point detection apparatus according to claim 7, whereinthe nanocarbon material includes a graphene sheet or a carbon nanotube.13. The polishing end point detection method according to claim 2,wherein the step of detecting the polishing end point of the polishingobject detects the polishing end point of the polishing object based ona change in intensity of a composite wave obtained by combining thelight reflected from a plurality of reflecting surfaces of the polishingobject and a polishing rate of the polishing object.
 14. The polishingend point detection method according to claim 2, wherein the step ofdetecting the polishing end point detects the polishing end point of thepolishing object based on a change in optical spectrum of the lightreflected from the polishing object.
 15. The polishing end pointdetection method according to claim 3, wherein the step of detecting thepolishing end point detects the polishing end point of the polishingobject based on a change in optical spectrum of the light reflected fromthe polishing object.
 16. The polishing end point detection apparatusaccording to claim 8, wherein the detection unit detects the polishingend point of the polishing object based on a change in intensity of acomposite wave obtained by combining the light reflected from aplurality of reflecting surfaces of the polishing object and a polishingrate of the polishing object.
 17. The polishing end point detectionapparatus according to claim 8, wherein the detection unit detects thepolishing end point of the polishing object based on a change in opticalspectrum of the light reflected from the polishing object.
 18. Thepolishing end point detection apparatus according to claim 9, whereinthe detection unit detects the polishing end point of the polishingobject based on a change in optical spectrum of the light reflected fromthe polishing object.